Alignment of an end of an optical fiber in relation to the output aperture of a laser chip must be made with a large accuracy in order to avoid optical losses when light is emitted from the laser which is to propagate along the fiber. The high accuracy raises the corresponding requirements on the assembly process, in particular when mounting the fiber at the appropriate position at the chip. Methods have been used for lowering the requirements on the accuracy when mounting the components such as using a method including a so called xe2x80x9ctaperedxe2x80x9d laser which has a mode field that is adapted to be used for coupling to for example a single mode optical fiber.
In existing assembly methods generally some kind of carrier is provided on which the optical fiber and the laser element in the shape of a chip are mounted. This carrier can be provided with different alignment means such as V-grooves, other types of grooves and furthermore accurately defined projections or bosses. Such a carrier can be produced as a silicon plate having anisotropically etched V-grooves produced therein and different layers deposited on the plate in order to form support surfaces, against which a chip can be accurately positioned.
In order to position an optoelectric chip on an intended place on the carrier also surface tension forces in molten solder areas, for example molten, small solder balls, which attach and possibly also electrically connect the chip to the carrier can be used, what can give a high accuracy when mounting a chip. Such a process requires great care when used and can therefore have limitations in obtaining a sufficiently high yield of correctly mounted components such as in demanding applications or in order to obtain a fabrication with a sufficient pay-off. The process depends on some delicate factors such as that the thickness of deposited solder should be maintained at a very constant value and that the areas which are wettable by the molten solder are accurately defined both on a chip and on the carrier.
Methods have been proposed using plastically deformable supports for the optical device or the optical fiber, the supports being deformed to making a final positioning or alignment of the fiber end in relation to the optical device. Thus, in the published International patent application WO 91/06022 a lens mount for a miniature optical lens is disclosed, the lens mount comprising a flat frame standing up from a base. The frame surrounds the portion where the lens is mounted and is capable of plastic deformation by bending the frame to an aligned position of the lens. Such a frame structure is not suited for aligning waveguides in or at a flat base with an optical component in a chip rigidly attached to the base. In addition the frame structure is space-consuming in the vertical direction.
Furthermore, in the published European patent application 0 717 297 fine alignment of an optical fiber with a laser chip is disclosed, using an elongate support member for retaining the fiber end. The support member has the shape of a cylinder rod comprising a longitudinal slot in which the fiber is held. The cylinder member is maintained at some distance from the base plate by a plastically deformable saddle having arms standing up from the base plate. The saddle arms can be deformed allowing a repositioning of the fiber end. This device is not well suited for finely moving a waveguide in or at a base plate into alignment with an opening of an optical component rigidly attached to the base. In addition the device is complicated and requires a plurality of mounting steps.
It is an object of the invention to provide a method and a carrier for optical building elements allowing an alignment of a surface area of an optical building element with a surface area of another optical building element.
It is a further object of the invention to provide a method and a carrier for optical building elements allowing an alignment of a surface area of an optical building element with a surface area of another optical building element using no extra mounting or attachment devices and thus not adding to the height of the total optical component.
It is a further object of the invention to provide a method and a carrier for optical building elements in an optical component allowing an alignment of input and output areas of the building elements with each other while simultaneously making a measurement of the feed-back type in order to obtain a maximum transmission between outputs and inputs.
The problem to be solved by the invention is how a good alignment between different optical building elements on a common carrier can be achieved. The problem comprises both achieving a fine alignment of for example optical components, which when finally tested have been decided to be erroneously mounted with an unsatisfactorily accuracy, and allowing a final, corrective alignment of the building elements in relation to each other, so that in the previous assembly process only a lower accuracy has to be maintained and thus a less costly assembly method can be used. Also, the problem comprises how a fine alignment can be made in a simple and space-consuming way.
An alignment method, which can also be called a final alignment method, is based on plastic deformation of a suitable material. This material is incorporated in a plateshaped carrier for optical building elements and the material of the carrier is thus to be selected so that it is plastically and mechanically deformable having a minimum elastic regression or spring back after a deformation having been made. The material should also be such that it is not influenced by subsequent steps when manufacturing an optical component, in particular not influenced by the sometimes rather high temperatures which can be required for example for curing encapsulating plastic or artificial resin materials. This condition can also be worded in the way that the material should have substantially no mechanical memory. The carrier can be made of copper plate having a high degree of purity, e.g. containing at least 99 per cent (wt.) of copper.
The carrier is configured so that it by means of exterior pressing surfaces can allow that certain portions, for example inner portions, of the carrier are displaced in different directions. In the case where an optical fiber attached to the carrier is to be aligned, appropriate portions of the carrier need to be displaced only in directions perpendicular to the longitudinal direction of the fiber. This deformation of the carrier can be executed after mounting different building elements thereon and it is further possible to measure the optical transmission between the different building elements attached to the carrier and to control the deformation of the carrier using feed-back so that a maximum optical transmission having thus a minimum attenuation is obtained between the inputs and outputs of the different optical building elements. The same method can also be used for producing a selected attenuation at the interface between two building elements in those cases where such an attenuation is desired, e.g. for adapting the input power to some light detector or light amplifier. The method can be generally described in the way that losses in the interface between two optical building elements, for example an optical fiber and a laser, can be measured during the alignment procedure, provided that one of the building elements is supplied with a suitable signal, for example by providing suitable electrical currents and voltages to a laser, so that it emits a light signal.
The carrier can be configured as a plate having suitably placed slots around that area of a building element which may have to be displaced in order to obtain a correct accurate alignment with another building element. The slots can for example have their longitudinal direction substantially perpendicular to those surfaces which are to be placed opposite each other and which in addition in a previous assembly procedure have been placed as close to or against each other as possible. The slots should also have portions extending in parallel to said areas and up to a region close thereto, so that a narrow region is formed in the vicinity of the surfaces, which region serves as weakened area and facilitates the deformation. Such slots will permit a displacement perpendicular to the plane of the carrier.
Additional objects and advantages of the invention will be set forth the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods, processes, instrumentalities and combinations particularly pointed out in the appended claims.